Output image adjustment of image data

ABSTRACT

A CPU calculates modified brightness correction amount tCurve_Y with consideration of exposure correction amount (or exposure value) EV if photography information PI (or Exif IFD) is included in image data GF. Specifically, the modified brightness correction amount tCurve_Y is calculated by dividing original brightness correction amount tCurve_Yorg by 2 |EV| . Therefore, it decreases in geometrical progression as the exposure correction amount increases. The CPU applies the obtained modified brightness correction amount tCurve_Y to a tone curve to adjust image quality including brightness. More specifically, it uses the modified brightness correction amount tCurve_Y to modify the characteristics of the tone curve, and then uses the modified tone curve to adjust the image quality of the image data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/512,894, filed Jun. 14, 2005, which is a national phase entry ofPCT/JP03/08874, filed Jul. 11, 2003. The disclosures of these priorapplications are hereby incorporated by reference in their entirety forall purposes.

TECHNICAL FIELD

The present invention relates to an image adjustment technique ofadjusting brightness of image data.

BACKGROUND OF THE INVENTION

The image quality of image data generated by a digital still camera(DSC), digital video camera (DVC), scanner or the like can bearbitrarily adjusted by use of an image-retouching application includedin a personal computer. The image-retouching application is generallyprovided with an image adjustment function of automatically adjustingimage quality (or characteristics) of image data, and this imageadjustment function makes it possible to readily adjust image quality ofimage data to be output from an output device into normal image quality.The output device of image data includes, for example, a CRT, a printer,a projector, a television receiver, and the like.

The printer driver for controlling operations of printer, which is oneof output devices, is also provided with a function of automaticallyadjusting image quality (or characteristics) of image data, and suchprinter driver makes it possible to readily adjust image quality ofimage data to be printed into normal image quality.

Typically, the automatic image quality adjustment function performed bythe image-retouching application and the like performs image qualitycorrection based on image quality of normal image data. However, sincethe image data subject to image processing can be generated under avariety of conditions, the automatic image quality adjustment functionmay result in poor image quality if the image quality (orcharacteristics) of image data is equally corrected using a referencevalue that is designed for the normal image data.

In addition, some image data generation devices such as DSC allow imagequality of image data to be arbitrarily adjusted during generation ofthe image data, and the user can intentionally generate image datahaving a predetermined image quality. If the automatic image qualityadjustment function is performed on such image data, intentional imagecharacteristics of the image data are also adjusted equally based on thereference value. Thus, there is a problem that in such cases it isimpossible to obtain an output image with the user's intention reflectedthereon.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the aboveproblems, and thus is intended to automatically adjust image quality ofimage data without diminishing an output tendency of intentional imageprocessing performed on the image data.

In order to solve the above problems, a first aspect of the presentinvention provides an image processing apparatus for using image dataand exposure correction amount for the image data to perform imageprocessing on the image data. The image processing apparatus accordingto the first aspect of the present invention includes a correctionamount determination module for determining brightness correction amountof the image data based on a brightness reference value that is used asa reference of image processing relating to brightness; a correctionamount modification module for decreasing the brightness correctionamount as the exposure correction value increases; and an image qualityadjustment module for applying the modified brightness correction amountto adjust brightness of the image data.

The image processing apparatus according to the first aspect of thepresent invention determines brightness correction amount of image databased on a brightness reference value that is used as a reference ofimage processing relating to brightness, modifies the determinedbrightness correction amount smaller as the exposure correction amountincreases, and applies the modified brightness correction amount toadjust brightness of the image data, and therefore enabling imagequality of image data to be automatically adjusted without diminishingan intentional output condition relating to brightness. Consequently,even if image quality is automatically adjusted, it is possible toobtain a brighter output result when the output result is intended to bebrighter, and to obtain a darker output result when the output result isintended to be darker.

In the image processing apparatus according to the first aspect of thepresent invention, the correction amount modification module may applydifferent degrees of change in the brightness correction amount to theexposure correction amount smaller than a predetermined exposurecorrection amount and the exposure correction amount larger than orequal to the predetermined exposure correction amount. Alternatively,the correction amount modification module may decrease the decreasingrate of the brightness correction amount as the exposure correctionamount increases. Such configurations ensure maintenance of the tone inhigh light areas and shadow areas even if the exposure correction amountincreases, and therefore preventing white clipping and black crushing.

In the image processing apparatus according to the first aspect of thepresent invention, the brightness correction amount may be decreased ingeometrical progression. In such case, even if image quality isautomatically adjusted, it is possible to obtain a brighter outputresult with more accuracy when the output result is intended to bebrighter, and to obtain a darker output result with more accuracy whenthe output result is intended to be darker. For example, the correctionamount modification module may modify the brightness correction amountby dividing the brightness correction amount by an exponential functionthat has the exposure correction amount as a parameter. In this case,the brightness correction amount can be decreased in geometricalprogression as the exposure correction amount increases.

The image processing apparatus according to the first aspect of thepresent invention may further include a brightness characteristic valueacquisition module for analyzing the image data to acquire a brightnesscharacteristic value indicating characteristics of brightness of theimage data, wherein the correction amount determination moduledetermines the brightness correction amount so as to reduce a differencebetween the brightness reference value and the acquired brightnesscharacteristic value. This enables characteristics relating tobrightness of the image data to be more properly corrected inconsideration of characteristics of each image data.

The image processing apparatus according to the first aspect of thepresent invention may further include an input module for inputting atendency of brightness correction for the image data, wherein thecorrection amount determination module determines brightness correctionamount of the image data based on the input tendency of brightnesscorrection. This enables characteristics relating to brightness of theimage data to be more properly corrected based on the input tendency ofbrightness correction.

The image processing apparatus according to the first aspect of thepresent invention may further include an image output module for usingthe brightness-adjusted image data to output an image. This enables theimage having corrected characteristics of brightness to be output.

In the image processing according to the first aspect of the presentinvention, the correction amount modification module may modify thebrightness correction amount in consideration of luminance differencebetween before and after contrast correction, and the image data and theexposure correction amount may be stored in a same file. This enableseffects on brightness due to the contrast correction to be compensated.In addition, this facilitates the exposure correction amount beingassociated with the image data.

A second aspect of the present invention provides an image processingapparatus for using image data and information on exposure correctionperformed on the image data to perform image processing on the imagedata. The image processing apparatus according to the second aspect ofthe present invention includes: a brightness characteristic valueacquisition module for analyzing the image data to acquire a brightnesscharacteristic value indicating characteristics of brightness of theimage data; an image quality adjustment module for reducing a differencebetween a brightness reference value that is used as a reference ofimage processing relating to brightness and the acquired brightnesscharacteristic value; and a reduced difference amount adjustment modulefor decreasing a degree of reduction in the difference based on theinformation on exposure correction increases as a degree of exposurecorrection performed on the image data.

The image processing apparatus according to the second aspect of thepresent invention, when reducing a difference between a brightnessreference value that is used as a reference of image processing relatingto brightness and the acquired brightness characteristic value,decreases a degree of reduction in the difference based on theinformation on exposure correction as a degree of exposure correctionperformed on the image data increases, and therefore enabling imagequality of image data to be automatically adjusted without diminishingan intentional output condition relating to brightness. Consequently,even if image quality is automatically adjusted, it is possible toobtain a desired brighter output result when the output result isintended to be brighter, and to obtain a desired darker output resultwhen the output result is intended to be darker. The degree of reductionin the difference may be decreased in geometrical progression. In suchcase, it is possible to obtain a desired brighter output result withmore accuracy when the output result is intended to be brighter, and toobtain a desired darker output result with more accuracy when the outputresult is intended to be darker.

The image processing apparatus according to the second aspect of thepresent invention may be configured as a method and a program inaddition to the above configuration, and may take a variety of aspectsas the image processing apparatus according to the first aspect of thepresent invention.

A third aspect of the present invention provides an image processingmethod for using image data and exposure correction amount for the imagedata to perform image processing on the image data. The image processingmethod according to the third aspect of the present invention includesthe steps of: determining brightness correction amount of the image databased on a brightness reference value that is used as a reference ofimage processing relating to brightness; modifying the brightnesscorrection amount smaller as the exposure correction amount increases;and applying the modified brightness correction amount to adjustbrightness of the image data.

The image processing method according to the third aspect of the presentinvention provides the same functions and effects as the imageprocessing apparatus according to the first aspect of the presentinvention. In addition, the image processing method according to thethird aspect of the present invention may take a variety of aspects asthe image processing apparatus according to the first aspect of thepresent invention.

A fourth aspect of the present invention provides a computer readablemedium storing an image processing program for using image data andexposure correction amount for the image data to perform imageprocessing on the image data. The image processing program stored in thecomputer readable medium according to the fourth aspect of the presentinvention causes the functions of: determining a brightness correctionamount of the image data based on a brightness reference value that isused as a reference of image processing relating to brightness;modifying the brightness correction amount smaller as the exposurecorrection amount increases; and applying the modified brightnesscorrection amount to adjust brightness of the image data.

The computer readable medium storing the image processing programaccording to the fourth aspect of the present invention provides thesame functions and effects as the image processing apparatus accordingto the first aspect of the present invention. In addition, the computerreadable medium storing the image processing program according to thefourth aspect of the present invention may take a variety of aspects asthe image processing apparatus according to the first aspect of thepresent invention.

A fifth aspect of the present invention provides an image processingapparatus for performing image processing on image data associated withphotography information indicating photography conditions at the time ofshooting. The image processing apparatus according to the fifth aspectof the present invention includes: an image quality characteristic valueacquisition module for analyzing acquired image data to acquire an imagequality characteristic value indicating characteristics of image qualityof the image data; a search module for searching the photographyinformation associated with the acquired image data for photographyinformation indicating an intention of photography; an image qualityadjustment module for reducing a difference between a predeterminedimage quality adjustment reference value that is used as a reference ofimage quality adjustment and the acquired image quality characteristicvalue to adjust image quality of the image data; and a reduceddifference amount adjustment module for using the searched photographyinformation indicating an intention of photography to adjust a degree ofreduction in the difference if the photography information indicating anintention of photography is detected.

The image processing apparatus according to the fifth aspect of thepresent invention can use photography information indicating anintention of photography among the photography information indicatingthe photography conditions at the time of shooting to adjust a degree ofreduction in the difference during the image quality adjustmentprocessing, and therefore enabling the image quality adjustmentprocessing with the intention of photography reflected thereon.

In the image processing apparatus according to the fifth aspect of thepresent invention, if the photography information indicating anintention of photography is not detected, a degree of reduction in thedifference may be not adjusted by use of the photography informationindicating an intention of photography. In such case, the image qualityadjustment processing can be performed without using photographyinformation indicating an intention of photography.

The fifth aspect of the present invention may take aspects including amethod and a recording medium storing a program in addition to the aboveconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram that shows one example of image processingsystem to which an image processing apparatus according to oneembodiment may be applied;

FIG. 2 is a block diagram that shows an outline configuration of adigital still camera capable of generating image data that may beprocessed by the image processing apparatus according to thisembodiment;

FIG. 3 is a block diagram that shows an outline configuration of a colorprinter that serves as the image processing apparatus according to thisembodiment;

FIG. 4 is a schematic diagram that shows an internal structure of animage file GF in the Exif format;

FIG. 5 is a schematic diagram that shows one example of detailedattribute information stored in the Exif IFD of the image file GF thatmay be used in this embodiment;

FIG. 6 is a flowchart that shows a processing routine of imageprocessing performed by the color printer 20 according to thisembodiment;

FIG. 7 is a flowchart that shows a processing routine of referencevalue-based automatic image quality adjustment processing performed bythe image processing apparatus (or color printer 20) according to thisembodiment;

FIG. 8 is a schematic diagram that shows the comparison of brightnesscorrection amount of the conventional method with that of the methodaccording to this embodiment;

FIG. 9 is a schematic diagram that shows one example of tone curvemodification performed during the brightness correction; and

FIG. 10 is a flowchart that shows a processing routine of imageprocessing added according to another embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The image processing apparatus according to the present invention isdescribed below based on embodiments with reference to the drawings.

A. Configuration of Image Processing System

A configuration of an image processing system to which the imageprocessing apparatus according to this embodiment may be applied isdescribed with reference to FIGS. 1 through 3. FIG. 1 is a schematicdiagram that shows one example of image processing system to which theimage processing apparatus according to this embodiment may be applied.FIG. 2 is a block diagram that shows an outline configuration of adigital still camera capable of generating image data that may beprocessed by the image processing apparatus according to thisembodiment. FIG. 3 is a block diagram that shows an outlineconfiguration of a color printer that serves as the image processingapparatus according to this embodiment.

An image processing system 10 includes a digital still camera 12 as aninput device for generating image data, a personal computer PC as theimage processing apparatus for performing image processing on the imagedata generated by the digital still camera 12, and a color printer 20 asan output device for outputting an image. Although the output device mayinclude a monitor 14 such as CRT display and LCD display, a projector,and the like as well as the printer 20, the color printer 20 is used asthe output device in the following description.

The digital still camera 12 electrically acquires an image by causingoptical information to form the image in a digital device (e.g. a CCD orphotomultiplier tube), and includes an optical circuit 121 that has theCCD or the like for collecting optical information, an image acquisitioncircuit 122 for controlling the optical circuit 121 to acquire theimage, an image processing circuit 123 for processing the acquireddigital image, and a control circuit 124 that has a memory fortemporarily storing each data and controls each of the circuits as shownin FIG. 2. The digital still camera 12 stores the acquired image asdigital data into a storage device such as memory card MC. Although thestorage format of image data in the digital still camera 12 is generallyJPEG format, other storage formats such as RAW, TIFF, GIF, and BMPformats may also be used.

The digital still camera 12 includes a selection/decision button 126 forsetting a shooting mode, exposure correction amount (or exposurecorrection value), light source, and the like, and a liquid crystaldisplay 127 for previewing shot images and for setting the exposurecorrection amount and the like using the selection/decision button 126.Since the digital still camera 12 automatically sets a proper exposure,the exposure correction amount set in the digital still camera 12 is setas positive or negative correction amount relative to the properexposure. The exposure correction amount, which is expressed in exposurevalue EV, is set to ±0 when the exposure is not corrected, is set to apositive value such as +0.1 EV and +2.0 EV when the exposure iscorrected higher relative to the proper exposure, and is set to anegative value such as −0.1 EV and −2.0 EV when the exposure iscorrected lower relative to the proper exposure.

The digital still camera 12 used within this image data output system 10stores, in addition to image data GD, photography information PI for theimage data as an image file GF into the memory card MC. Morespecifically, at the time of shooting, the photography information PI isautomatically stored as the image file GF along with the image data GDinto the memory card MC. For example, if photography parameters such asexposure correction amount, light source, and the like have been set toarbitrary values by the user, the image file GF including the image dataGD generated according to the set exposure correction amount and thephotography information PI in which the values of the set parameters aredescribed is stored into the memory card MC.

The image file GF generated by the digital still camera 12 istransmitted to the color printer 20, for example, via a cable CV and thecomputer PC, or via the cable CV. Alternately, the image file istransmitted to the printer 20 via the computer PC having the memory cardMC inserted in the memory card slot on which the image file GF wasstored by the digital still camera 12, or via a direct connection of thememory card MC to the printer 20. In this embodiment, the description ismade based on the case where the color printer 20 performs imageprocessing and output (print) processing in stand-alone fashion.

The color printer 20 shown in FIG. 3 is capable of outputting colorimages, for example, a jet ink type printer which ejects inks of fourcolors including cyan (C), magenta (M), yellow (Y) and black (K) onto aprinting medium to form a dot pattern and thus an image. Alternately,the color printer 20 may include an electro-photographic type printerwhich transfers and fixes color toner on a printing medium to form animage. In addition to the above four colors, the color inks may includelight cyan (LC), light magenta (LM), and dark yellow (DY).

The color printer 20 includes a print unit 21 that has a print head, arotating drum or the like and performs print processing on the printingmedium, a slot 22 for containing the memory card MC, and a controlcircuit 23 for controlling an operation of each unit of the colorprinter 20. The control circuit 23 includes a central processing unit(CPU) 231 for performing a variety of arithmetic processing, a read-onlymemory (ROM) for storing in a nonvolatile fashion a program performed bythe CPU 231 and other data, and a random access memory (RAM) 233 fortemporarily storing a result of arithmetic processing performed by theCPU 231 and acquired data. The control circuit 23 analyzes thephotography information PI read out from the memory card MC to controloperations of a paper feed motor, a carriage motor, a print head, andthe like (not shown) based on the analyzed photography information PI.

B. Configuration of Image File

The image file GF according to this embodiment can have, for example, afile structure according to an image file format standard (Exif) fordigital still cameras. The specifications of Exif files, which areestablished by Japan Electronics and Information Technology IndustriesAssociation (JEITA), include a JPEG-Exif file in which the image data isstored as JPEG data of compressed type and a TIFF-Exif file in which theimage data is stored as TIFF data of uncompressed type. In the followingdescription, the compressed file or JPEG-Exif file is used.

The outline configuration of the image file in the Exif format that maybe used in this embodiment is described with reference to FIG. 4. FIG. 4is a schematic diagram that shows an internal structure of the imagefile GF in the Exif format. The terms such as file structure, datastructure, and storage area in this embodiment depict images of file,data or the like that is stored within the storage device.

The image file GF includes a SOI marker segment 101 indicating a startof the compressed data, an APP1 marker segment 102 storing Exifattribute information, an APP2 marker segment 103 storing Exif extendedinformation, a DQT marker segment 104 defining a quantization table, aDHT marker segment 105 defining a Huffman table, a DRI marker segment106 defining an interval at which restart markers are inserted, a SOFmarker segment 107 indicating a variety of parameters relating toframes, a SOS marker segment 108 indicating a variety of parametersrelated to scans, and an EOI marker segment 109 indicating an end of thecompressed data. The compressed data GD is stored in an image datastorage area 110 between the SOS marker segment 108 and the EOI markersegment 109. The sequence in which the marker segments are recorded isarbitrary as long as the APP1 and then the APP2 marker segments arerecorded just after the SOI marker segment and the SOS marker segment isrecorded across the image data just before the EOI marker segment.

The APP1 marker segment 102 consists of an APP1 marker 1021, an Exifidentifier code 1022, attribute information 1023, and a thumbnail image1024. The attribute information take a TIFF structure including a fileheader (or TIFF header), and in the case of Exif-JPEG include a 0th IFDfor storing attribute information relating to the compressed image data,an Exif IFD for storing Exif-specific attribute information such as thephotography information PI, and a 1st IFD for storing attributeinformation relating to the thumbnail image. The Exif IFD is pointed toby the offset from the TIFF header stored in the 0th IFD. The IFDs use atag to identify each information, which may be represented by a tagname.

The photography information PI is information (or image qualitygeneration information) relating to image quality when the image datawas generated (or shot) by an image data generation device such as thedigital still camera 12, and may include parameters relating to theexposure time, the ISO sensitivity, the aperture, the shutter speed andthe focus distance which are automatically recorded at the time ofshooting, and parameters relating to the exposure correction amount, thelight source, the shooting mode, and the like which are arbitrarily setby the user.

The detailed attribute information stored in the Exif IFD are describedwith reference to FIG. 5. FIG. 5 is a schematic diagram that shows oneexample of the detailed attribute information stored in the Exif IFD ofthe image file GF that may be used in this embodiment.

The Exif stores tags of Exif version information, color spaceinformation, date and time of image data generation, and photographyconditions. The tag relating to photography conditions (or photographyinformation) stores parameter values such as exposure time, lens Fnumber, exposure control mode, ISO sensitivity, exposure correctionamount, light source; white valance, flash, focus distance, and the likeaccording to predetermined offsets. The image processing apparatus (oroutput device) can specify an offset corresponding to a desired taginformation (or parameter) to acquire a desired photography informationPI.

C. Image Processing by Color Printer 20

The image processing performed by the color printer 20 is describedbelow in detail with reference to FIGS. 6 through 8. FIG. 6 is aflowchart that shows a processing routine of the image processingperformed by the image processing apparatus (or color printer 20)according to this embodiment. FIG. 7 is a flowchart that shows aprocessing routine of reference value-based image quality adjustmentprocessing (or automatic image quality adjustment processing) performedby the image processing apparatus (or color printer 20) according tothis embodiment. FIG. 8 is a schematic diagram that shows the comparisonof brightness correction amount of the conventional method with that ofthe method according to this embodiment.

When the memory card MC is inserted into the slot 22, the controlcircuit 23 (or CPU 231) of the color printer 20 reads out the image fileGF from the memory card MC, and temporarily stores it into the RAM 233(step S100). The CPU 231 expands the image data GD contained in the readimage file GF, and then performs a matrix calculation with a matrix S onthe expanded image data GD to perform YCbCr to RGB color conversionprocessing (step S110).

As described above, the image file GF in this embodiment stores imagedata in JPEG file format as the image data GD, and the image data inJPEG file format is compressed YCbCr data. Recently, image processingperformed by personal computers PC and printers generally uses RGB data.Therefore, it is necessary to expand (or decode) the image data in JPEGfile format and to perform color conversion processing from YCbCr datato RGB data. The matrix S is generally used to convert YCbCr data intoRGB data in JFIF format that establishes specifications of JPEG file,and is not described any further since it is well known to a personskilled in the art.

The CPU 231 performs the reference value-based image quality adjustmentprocessing on the RGB data obtained through the conversion (step S120).The reference value-based image quality adjustment processing, which isgenerally referred to as automatic image quality adjustment processing,does not depend on external input and uses preferred normal parametervalues (or reference values) stored within the ROM 232 in advance toadjust image quality. The parameters used for this image qualityadjustment include, for example, parameters relating to image qualitysuch as brightness, sharpness, and the like, and normal parameter valuesrelating to these parameters are used to calculate correction amount,which is then applied to the image adjustment. The details will bedescribed later with reference to FIG. 7.

The CPU 231 performs a color conversion processing to convert the imagedata (or RGB data) having undergone the automatic image qualityadjustment processing into CMYK data (step S130). That is, the colorsystem of the image data is converted into the CMYK color system used bythe color printer 20 to perform print processing. Specifically, thisconversion is performed using a look-up table that is stored in the ROM232 and that associates the RGB color system with the CMYK color system.

When the CPU 231 completes the above image processing, it uses theobtained image data to perform print output processing (step S140), andthen exits this processing routine. In the print output processing, theCPU 231 performs the halftone processing and the resolution conversionprocessing, and then sends the processed data in the form of raster datato the print unit 21.

The automatic image quality adjustment processing is described below indetail with reference to FIG. 7. The CPU 231 analyzes the image data(step S200). More specifically, in the automatic image qualityadjustment processing according to this embodiment, the CPU analyzes theimage data GD on a pixel-by-pixel basis to acquire a variety ofcharacteristic parameter values indicating characteristics of the imagedata GD, such as image statistics of minimum luminance, maximumluminance, and brightness representative value. Since the image data GDis RGB data at this point of time, the minimum luminance Ymin, themaximum luminance Ymax, and the like are acquired using an equation ofY=0.30R+0.59G+0.11B.

The CPU 231 uses the minimum luminance Ymin and the maximum luminanceYmax to perform level correction (or contrast correction) (step S210).Specifically, given that the RGB components of the original image dataGD are R, G, and B while the corrected RGB components are R′, G′, andB′, the correction is performed on each pixel using an equation of (R′,G′, B′)=255*(R, G, B)(Ymax−Ymin) Ymin. The CPU 231 calculates luminancedifference ΔY=Ymod−Yorg between the luminance value at the 128 point ofthe original image data (i.e. image data before the level correction)and the luminance value Ymod at the 128 point of the corrected imagedata (step S220). The 128 point is one of horizontal axis points (i.e.input values) of a tone curve where a horizontal axis represents inputvalues of image data (i.e. original image data) and a vertical axisrepresents output values of image data (i.e. corrected image data).Although the level correction is performed after the conversion to RGBdata, such processing may be performed using luminance components Y atthe stage of YCbCr data.

The CPU 231 uses the following equation 1 to calculate originalbrightness correction amount (brightness correction amount withoutconsideration of exposure correction amount) tCurve_Yorg (step S230).

tCurve_(—) Y _(ORG)=2*√{square root over (B _(ref) −B_(smp))}  (Equation 1)

For example, if the brightness reference value Bref is equal to 128 andthe brightness representative value Bsmp obtained through the sampling(i.e. analysis) is equal to 56, tCurve_Yorg is equal to 16 as shown inFIG. 8. The brightness reference value Bref is, for example, 8-bitinformation that can take a value ranging from 0 to 255, and is set to128 in this embodiment.

The CPU 231 determines whether or not the photography information PI(Exif IFD) is included in the image data GF (step S240), and if itdetermines that the photography information PI is included (Yes at stepS240), then it calculates modified brightness correction amount tCurve_Ywith consideration of the exposure correction amount (or exposure value)EV (step S250). The modified brightness correction amount tCurve_Y iscalculated by the following equation 2.

$\begin{matrix}{{tCurve\_ Y} = {\frac{{tCurve\_ Y}_{ORG}}{2^{{EV}}} + {\Delta \; Y}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In Equation 2, the luminance difference ΔY is a correction term forcompensating for the effect on the brightness of the image data GD dueto the contrast (level) correction. If the luminance difference ΔY isopposite in sign to the exposure correction amount EV, the luminancedifference ΔY=0 is used to calculate the modified luminance correctionamount tCurve_Y. In this case, since the photographer's intentionrelating to exposure is opposed to the direction of the automaticcorrection, the compensation value caused by the contrast correction isnot applied so as to give preference to the photographer's intention.

The CPU 231 applies the obtained modified brightness correction amounttCurve_Y to the tone curve to adjust the image quality including thebrightness (step S260), and then exits this processing routine. Morespecifically, it uses the modified brightness correction amount tCurve_Yto modify the characteristics of the tone curve, and then uses themodified tone curve to correct (or change) output values (or outputlevel) of R, G, and B components of the image data GD for each pixel.

If the CPU 231 determines that the photography information PI is notincluded (No at step S240), it cannot make consideration of exposurecorrection amount (or exposure value) EV, and thus applies the originalbrightness correction amount tCurve_Yorg to the tone curve to adjust theimage quality including the brightness (step S270) and then exits thisprocessing routine.

The modification of the tone curve characteristics using the modifiedbrightness correction amount tCurve_Y or the original brightnesscorrection amount tCurve_Yorg is performed, for example, as shown inFIG. 9. FIG. 9 is a schematic diagram that shows one example of tonecurve modification performed during the brightness correction. If theexposure correction amount EV is a positive value, that is, thephotographer desires to increase the brightness through the correction,output levels OL1 and OL2 are raised at the 1/4 point of input levelaccording to the brightness correction amount, for example. On the otherhand, if the exposure correction amount EV is a negative value, that is,the photographer desires to decrease the brightness through thecorrection, the output level OL3 is lowered at the 3/4 point of inputlevel according to a corrected level, for example. Values other than thepoint corresponding to the corrected level are interpolated with aspline curve.

FIG. 8 shows the comparison of the brightness correction amount obtainedby use of the color printer 20 according to this embodiment with thoseobtained by use of the conventional method. Here, the brightnesscorrection of the conventional method is a method of calculating thebrightness correction amount by changing the brightness reference valueBref according to the exposure correction amount EV in the aboveequation 1. For example, if a standard value of the brightness referencevalue Bref is equal to 128, the brightness reference value Bref ismodified by calculating a value using a conversion equation of 0.1 EV=2(brightness modification value) relative to the standard value andadding the calculated value to the brightness standard value of 128.More specifically, Bref=‘standard value’+(2×‘exposure correction amountEV’/0.1), and therefore the brightness modification value is added tothe standard value in the case of positive exposure correction amount EVwhile the brightness modification value is subtracted from the standardvalue in the case of negative exposure correction amount EV.

For example, if the brightness representative value Bsmp is equal to 56and the exposure correction amount EV is equal to −1.0, the brightnessreference value Bref is modified from 128 to 108, the modifiedbrightness reference value causes the brightness correction amount to beequal to 14. In another example, if the brightness representative valueBsmp is equal to 56 and the exposure correction amount EV is equal to−2.0, the brightness reference value Bref is modified from 128 to 108,the modified brightness reference value causes the brightness correctionamount to be equal to 11.

On the other hand, according to the color printer 20 of this embodiment,if the luminance difference ΔY is equal to +5, the brightnessrepresentative value Bsmp is equal to 56, and the exposure correctionamount EV is equal to −1.0, applying these values to the equation 2causes the modified brightness correction amount to be equal to 8. Inanother example, if the luminance difference ΔY is equal to +5, thebrightness representative value Bsmp is equal to 56, and the exposurecorrection amount EV is equal to −2.0, applying these values to theequation 2 causes the modified brightness correction amount tCurve_Y tobe equal to 4.

In this manner, the color printer 20 (or image processing apparatus)according to this embodiment can reflect the photography information PIcontained in the image file GF to automatically adjust the brightness ofimage data GD. Therefore, if the user has arbitrarily set a tendency ofimage output, the automatic image adjustment processing is preventedfrom performing the image adjustment, and thereby ensuring the automaticimage adjustment processing that reflects the user's intention.

In particular, the color printer 20 according to this embodimentcorrects the brightness correction amount by dividing the brightnesscorrection amount without consideration of the exposure correctionamount EV by 2^(|EV|), and therefore can perform the brightnesscorrection that is better adapted to the photographer's intention thanthe conventional method. That is, as the absolute value of the exposurecorrection amount increases, the modified brightness correction amounttCurve_Y can be significantly decreased in geometrical progression (orexponentially). Therefore, the color printer 20 can reflect thephotographer's intention of brightening or darkening the output resulton the output result of the image data with more accuracy.

In addition, the color printer 20 according to this embodiment corrects(or modifies) the brightness correction amount in consideration of theluminance difference ΔY between before and after the contrast correction(or level correction), and therefore can compensate effect on thebrightness due to the contrast correction. Therefore, if the contrastcorrection is performed, the brightness correction can be adapted to thephotographer's intention.

Furthermore, the image quality can be automatically adjusted with theaid of the photography information PI contained in the image file GF,and therefore enabling the printing result of high quality on which theuser's intention of the photograph is reflected to be readily obtainedwithout performing image quality adjustment by use of a photo-retouchingapplication or printer driver.

Other Embodiments

Although the reference value-based image quality adjustment processingis performed after the YCbCr to RGB color conversion processing in theimage processing of the embodiment described above, additionalprocessing may be performed as shown in FIG. 10. FIG. 10 is a flowchartthat shows a processing routine of image processing added according toanother embodiment. Here, the steps including the YCbCr to RGB colorconversion processing (step 5110) and the preceding steps, and the stepsincluding the reference-based image quality adjustment processing (stepS120) and the following steps are not described since they have beendescribed.

The CPU 231 performs the gamma correction on the image data converted toRGB data to linearize the image data prior to the following colorconversion process (step S111). The gamma value used for the gammacorrection is specific to the digital still camera, and may be acquiredbased on a parameter of the photography information PI or may besupplied as image processing information associated with the image dataGD besides the photography information PI.

The CPU 231 uses a matrix to perform color conversion processing forconverting RGB data into wRGB data (step S112). The wRGB color space hasat least partly broader areas than the sRGB color space generally used,and preferably encompasses the sRGB color space. Using such wide RGBcolor space enables the CPU 231 to proceed to the subsequent automaticimage quality adjustment processing without losing any value of the RGBdata converted from YCbCr data. The matrix used for this colorconversion is a combined matrix N-¹M of a matrix such as matrix M forconverting RGB data into XYZ data and a matrix such as matrix N forconverting wRGB data into XYZ data, or a matrix M and a matrix N-¹.

The CPU 231 performs the inverse gamma correction on the image dataconverted to wRGB data (step S113). The gamma value used for thisinverse gamma correction is specific to the color printer 20, and isstored in advance, for example, in the ROM 232. Such inverse gammacorrection enables the image data GD to generated taking into accountthe gamma characteristic of the color printer 20.

The CPU 231 sequentially performs the automatic image quality adjustmentprocessing (step S120) and the following steps described above. Thisembodiment enables the automatic image quality adjustment processing tobe performed without losing any value of the RGB data converted from theYCbCr data, and therefore ensuring more proper image quality adjustmentprocessing.

Although the image quality adjustment processing of brightness isautomatically performed based on the single reference value in theembodiment described above, the color printer 20 may be provided on itscontrol panel with automatic image quality adjustment buttons forselecting a tendency of brightness correction such as ‘brighter’ and‘darker’ so that the brightness reference value Bref and thus thebrightness correction amount are modified according to the tendency ofbrightness correction selected through such automatic image qualityadjustment buttons.

Although the image quality adjustment processing is automaticallyperformed in the embodiment described above, the color printer 20 may beprovided on its control panel with automatic image quality adjustmentbuttons so that the automatic image quality adjustment processing of theabove embodiments is performed only if the automatic image qualityadjustment selected through such automatic image quality adjustmentbuttons is selected.

Although the color printer 20 performs the entire image processingwithout using the personal computer PC, and then forms a dot patternonto the printing medium according to the generated image data GD in theembodiment described above, the computer may perform all or part of theimage processing. This is actualized by providing the image processingfunctions described with reference to FIGS. 6 through 8 for image dataprocessing applications such as retouching application and printerdriver installed on a hard disk and the like of the computer. The imagefile GF generated by the digital still camera 12 is supplied to thecomputer via a cable or the memory card MC. On the computer, the user'soperations cause the application to be activated, and then reading ofthe image file GF, analysis of the photography information PI, andconversion and adjustment of the image data GD to be performed.Alternatively, detecting the insertion of memory card MC or cable maycause the application to be automatically actualized, and then readingof the image file GF, analysis of the photography information PI, andconversion and adjustment of the image data GD to be automaticallyperformed.

In addition, all or part of the image processing performed by thepersonal computer PC may be performed by the digital still camera 12.This is actualized by providing the image processing functions describedwith reference to FIGS. 6 through 8 for image data processingapplications such as retouching application and printer driver stored ona ROM and the like of the digital still camera 12. Print data includingprint control commands and print image data generated by the digitalstill camera 12 is supplied to the printer 20 via a cable or the memorycard MC. When the printer 20 receives the print data, it forms a dotpattern onto a printing medium according to the print image data tooutput an image. The digital still camera 12 may supply the print imagedata (image data having undergone the image processing) to the personalcomputer PC or the printer 20. In such case, the personal computer PC orthe printer 20 provides the print image data with the print controlcommands.

Although the automatic image quality adjustment has been described withreference to the brightness correction considering the exposurecorrection amount in the embodiment described above, the automatic imagequality adjustment can reflect the photography information PI on anothercharacteristic parameter value of the image data GD such as shadowcontrast point, contrast, color balance, saturation, and sharpness.

In addition, a characteristic parameter value on which the automaticimage quality adjustment is performed may be selectable. For example,the color printer 20 is provided with selection buttons for selecting aparameter, or with selection buttons for selecting a shooting modeparameter in which predetermined parameters are combined based on anobject of shooting so that the parameter on which the automatic imagequality adjustment is performed is selected through these selectionbuttons. Alternatively, when the automatic image quality adjustment isperformed by the personal computer, the parameter on which the automaticimage quality adjustment is performed may be selected through a userinterface of the printer driver or the retouching application.

Although the brightness correction amount is decreased in geometricalprogression as the exposure correction amount increases in theembodiment described above, different degrees of change in thebrightness correction amount may be applied to the exposure correctionamount being smaller than a predetermined exposure correction amount andthe exposure correction amount being larger than or equal to thepredetermined exposure correction amount. Alternatively, the decreasingrate of brightness correction amount may be decreased as the exposurecorrection amount increases. In such cases, it is also possible tomaintain the tone in high light areas and shadow areas even if theexposure correction amount increases, and therefore preventing whiteclipping and black crushing.

Although the color printer 20 is used as an output device in theembodiments described above, the output device may include displaydevices such as CRT, LCD, projector, and the like. In such case, thedisplay device as the output device performs, for example, an imageprocessing program (or display driver) for performing the imageprocessing described with reference to FIGS. 6 through 8. Alternatively,if the CRT or the like serves as the display device of the computer, thecomputer performs the image processing program. However, the image datathat is finally output does not have a CMYK color space but a RGB colorspace.

In such case, the photography information PI at the time of image datageneration can be reflected on a displaying result caused by the displaydevice such as CRT and the like, as reflected on a printing resultcaused by the color printer 20. Therefore, this ensures more accuratedisplay of the image data GD generated by the digital still camera 12.

Although the Exif format file is taken as a concrete example of imagefile GF in the embodiment described above, the format of image fileaccording to the present invention is not limited to this format. Thatis, any image file may be used as long as it includes image data GD andinformation on exposure correction associated with the image data GD.The information on exposure correction may be the photographyinformation PI of the image data or image processing control informationfor controlling the image processing apparatus in a more active manner.The parameters shown in FIG. 8 that are stored as the photographyinformation PI in the above embodiment are only exemplary, and thus avariety of parameters according to Exif standard can be stored.

The digital still camera 12 and the color printer 20 used in the aboveembodiment are only exemplary, and thus their configurations are notlimited to the details described with regard to each embodiment. Thedigital still camera 12 suffices as long as it has at least the functionof generating the image file GF according to the above embodiment. Thecolor printer 20 suffices as long as it is at least capable of analyzingthe photography information PI of the image file GF according to thisembodiment, automatically adjusting image quality with reflecting theuser's intention especially relating to brightness, and outputting (orprinting) the image.

Although the image data GD and the photography information PI areincluded in the same image file GF in the embodiment described above,the image data GD and the photography information PI are not necessarilystored in the same file. That is, it suffices to associate the imagedata GD with the photography information PI (or image processing controlinformation). For example, it is applicable that association data aregenerated to associate image data GD with photography information PI (orimage processing control information), one or more image data GD andphotography information PI are stored into the respective separatefiles, and the associated photography information PI is referred inorder to process the image data GD. In this case, during the imageprocessing that uses the photography information PI, the image data andthe photography information PI are inseparably related, andsubstantially have the same function as in the case where they arestored in the same file. In addition, the image file GF also includes amoving image file stored in an optical disk medium such as CD-ROM, CD-R,DVD-ROM, DVD-RAM, and the like.

Hereinabove the image processing apparatus according to the presentinvention has been described based on the several embodiments. However,the above embodiments of the invention are intended to facilitate abetter understanding of the present invention and do not limit thepresent invention. The present invention may be modified and improvedwithout departing from the spirit and the scope of claim for patent, andincludes equivalents thereof.

1. An image processing apparatus for using image data and exposurecorrection amount for the image data to perform image processing on theimage data, the image processing apparatus comprising: a correctionamount determination module for determining brightness correction amountof the image data based on a brightness reference value that is used asa reference of image processing relating to brightness; a correctionamount modification module for decreasing the brightness correctionamount as the exposure correction amount increases; and an image qualityadjustment module for applying the modified brightness correction amountto adjust brightness of the image data.
 2. An image processing apparatusaccording to claim 1, wherein the correction amount modification moduleapplies different degrees of change in the brightness correction amountto the exposure correction amount smaller than a predetermined exposurecorrection amount and the exposure correction amount larger than orequal to the predetermined exposure correction amount.
 3. An imageprocessing apparatus according to claim 1, wherein the correction amountmodification module decreases the decreasing rate of the brightnesscorrection amount as the exposure correction amount increases.
 4. Animage processing apparatus according to claim 2, wherein the correctionamount modification module decreases the brightness correction amount ingeometrical progression as the exposure correction amount increases. 5.An image processing apparatus according to claim 4, wherein thecorrection amount modification module divides the brightness correctionamount by an exponential function that has the exposure correctionamount as a parameter.
 6. An image processing apparatus according toclaim 5, further comprising: a brightness characteristic valueacquisition module for analyzing the image data to acquire a brightnesscharacteristic value indicating characteristics of brightness of theimage data, wherein the correction amount determination moduledetermines the brightness correction amount so as to reduce a differencebetween the brightness reference value and the acquired brightnesscharacteristic value.
 7. An image processing apparatus according toclaim 5, further comprising: an input module for inputting a tendency ofbrightness correction for the image data, wherein the correction amountdetermination module determines brightness correction amount of theimage data based on the input tendency of brightness correction.
 8. Animage processing apparatus according to claim 6, further comprising: animage output module for using the brightness-adjusted image data tooutput an image.
 9. An image processing apparatus according to claim 1wherein the correction amount modification module modifies thebrightness correction amount in consideration of a luminance differencebetween before and after contrast correction, and the image data and theexposure correction amount are stored in a same file.
 10. An imageprocessing apparatus for using image data and information on exposurecorrection performed on the image data to perform image processing onthe image data, the image processing apparatus comprising: a brightnesscharacteristic value acquisition module for analyzing the image data toacquire a brightness characteristic value indicating characteristics ofbrightness of the image data; an image quality adjustment module forreducing a difference between a brightness reference value that is usedas a reference of image processing relating to brightness and theacquired brightness characteristic value; and a reduced differenceamount adjustment module for decreasing a degree of reduction in thedifference based on the information on exposure correction increases asa degree of exposure correction performed on the image data.
 11. Animage processing apparatus according to claim 10, wherein the correctionamount modification module applies different degrees of change in thebrightness correction amount to the exposure correction amount smallerthan a predetermined exposure correction amount and the exposurecorrection amount larger than or equal to the predetermined exposurecorrection amount.
 12. An image processing apparatus according to claim10, wherein the correction amount modification module decreases thedecreasing rate of the brightness correction amount as the exposurecorrection amount increases.
 13. An image processing apparatus accordingto claim 12, wherein a degree of reduction in the difference isdecreased by the reduced difference amount adjustment module ingeometrical progression.
 14. An image processing apparatus according toclaim 10, wherein the image data and the information on exposurecorrection are stored in a same file.
 15. An image processing method forusing image data and exposure correction amount for the image data toperform image processing on the image data, the method comprising:determining brightness correction amount of the image data based on abrightness reference value that is used as a reference of imageprocessing relating to brightness; modifying the brightness correctionamount smaller as the exposure correction amount increases; and applyingthe modified brightness correction amount to adjust brightness of theimage data.
 16. An image processing method according to claim 15,wherein in the modifying the brightness correction amount, differentdegrees of change in the brightness correction amount are applied to theexposure correction amount smaller than a predetermined exposurecorrection amount and the exposure correction amount larger than orequal to the predetermined exposure correction amount.
 17. An imageprocessing method according to claim 15, wherein the decreasing rate ofthe brightness correction amount is decreased as the exposure correctionamount increases.
 18. An image processing method according to claim 17,wherein the brightness correction amount is modified smaller ingeometrical progression.
 19. An image processing method according toclaim 15, further comprising: analyzing the image data to a brightnesscharacteristic value indicating characteristics of brightness of theimage data; determining the brightness correction amount so as to reducea difference between the brightness reference value and the acquiredbrightness characteristic value; and dividing the determined brightnesscorrection amount by an exponential function that has the exposurecorrection amount as a parameter.
 20. An image processing methodaccording to claim 15, further comprising: receiving a tendency ofbrightness correction for the image data; determining brightnesscorrection amount of the image data based on the received tendency ofbrightness correction; and dividing the determined brightness correctionamount by an exponential function that has the exposure correctionamount as a parameter.
 21. A computer readable medium storing an imageprocessing program for using image data and exposure correction amountfor the image data to perform image processing on the image data, theimage processing program causing a computer to implement the functionsof: determining brightness correction amount of the image data based ona brightness reference value that is used as a reference of imageprocessing relating to brightness; modifying the brightness correctionamount smaller as the exposure correction amount increases; and applyingthe modified brightness correction amount to adjust brightness of theimage data.
 22. A computer readable medium according to claim 21,wherein the function of modifying the brightness correction amountapplies different degrees of change in the brightness correction amountto the exposure correction amount smaller than a predetermined exposurecorrection amount and the exposure correction amount larger than orequal to the predetermined exposure correction amount.
 23. A computerreadable medium according to claim 21, wherein the decreasing rate ofthe brightness correction amount is decreased as the exposure correctionamount increases.
 24. A computer readable medium according to claim 23,wherein the brightness correction amount is decreased in geometricalprogression.
 25. A computer readable medium according to claim 21, theimage processing program further causing the computer to implement thefunction of: analyzing the image data to acquire a brightnesscharacteristic value indicating characteristics of brightness of theimage data, wherein the function of determining the correction amountdetermines the brightness correction amount so as to reduce a differencebetween the brightness reference value and the acquired brightnesscharacteristic value, and the function of modifying the brightnesscorrection amount divides the determined brightness correction amount byan exponential function that has the exposure correction amount as aparameter.
 26. A computer readable medium according to claim 21, theimage processing program further causing the computer to implement thefunction of: inputting a tendency of brightness correction for the imagedata, wherein the function of determining the correction amountdetermines brightness correction amount of the image data based on theinput tendency of brightness correction, and the function of modifyingthe brightness correction amount divides the determined brightnesscorrection amount by an exponential function that has the exposurecorrection amount as a parameter.
 27. A computer readable mediumaccording to claim 21, the image processing program further causing thecomputer to implement the function of: outputting thebrightness-adjusted image data to an output device.
 28. An imageprocessing apparatus for performing image processing on image dataassociated with photography information indicating photographyconditions at the time of shooting, the image processing apparatuscomprising: an image quality characteristic value acquisition module foranalyzing acquired image data to acquire an image quality characteristicvalue indicating characteristics of image quality of the image data; asearch module for searching the photography information associated withthe acquired image data for photography information indicating anintention of photography; an image quality adjustment module forreducing a difference between a predetermined image quality adjustmentreference value that is used as a reference of image quality adjustmentand the acquired image quality characteristic value to adjust imagequality of the image data; and a reduced difference amount adjustmentmodule for using the searched photography information indicating anintention of photography to adjust a degree of reduction in thedifference if the photography information indicating an intention ofphotography is detected.
 29. An image processing apparatus according toclaim 28, wherein if the photography information indicating an intentionof photography is not detected, a degree of reduction in the differenceis not adjusted by use of the photography information indicating anintention of photography.